Recent sliding devices have been needed to meet anticipated design specifications in extensively increased fields as diverse as semiconductor industries, various assembling machines, precise measuring/inspection equipments, testing machines, machine tools, and so on. An example of the small sliding device with onboard linear motor is disclosed in, for example Japanese Patent Laid-Open No. H09-266659 in which a moving table is made of magnetic material including steel, and so on and is installed thereon with field magnets to serve as a magnet yoke for magnetic circuit, while a stationary bed is also made of magnetic material to serve as a magnet yoke for magnetic circuit of armature windings.
Disclosed in Japanese Patent Laid-Open No. 2002-10617 is a sliding device with onboard moving-magnet, which is made smaller in construction and higher in propulsion as well as in speed response, compared with the small sliding device with onboard linear motor as recited earlier. With the prior sliding device recited here, an auxiliary magnet is placed out of N-pole of forward and aft magnetic end poles of the field magnet to makes up for the magnetic flux pattern at the end pole of the field magnet, thereby getting the magnetic sensor element detect an accurate position of the field magnet. Moreover, accurate position of the moving table is sensed by means of the magnetic sensor element that is arranged on the stationary bed in opposition to the field magnet. The auxiliary magnet is magnetized in a polarity unlike the associated end pole of the field magnet and made less in size to minimize the influence owing to the interaction of the armature windings with the auxiliary magnet on the propulsion given to the moving table from the field magnet. The auxiliary magnet constructed as stated above serves to rectify the magnetic flux pattern at the end pole of the field magnet, which might otherwise deviate outwardly, thereby making sure of the same magnetic flux pattern as in the magnetic flux found at a boundary between any two adjacent magnetic poles in the field magnet. Thus, this auxiliary magnet makes it possible to sense any end pole of the field magnet with the same accuracy as at the boundary between the two adjacent poles in the field magnet. The stationary bed and moving table are both made of magnetic material while the field magnets made of rare earth magnet are placed on the moving table. Besides the auxiliary magnet, there are arranged an end plate and a sensor magnet on the moving table, while the stationary bed has thereon an armature assembly for three-phase conduction system. The prior sliding device is envisaged making the sliding device small in construction even with high in propulsion and speed response. Moreover, there is provided an optical encoder to ensure highly accurate position control.
With the small sliding device disclosed in the first citation, which is co-pending senior application of common assignment, nevertheless, a recess cut underneath the moving table to secure the field magnets to the moving table is made as deep as the thickness of the field magnet. Even though the field magnet is getting smaller to have up to five poles, the recess remains deep and therefore the magnetic flux of the field magnet fit into the recess would leak out to side walls of the associated recess. If that happens, the magnetic flux heading toward the armature windings might become less intense so that the propulsion to thrust the moving table would result in getting reduced remarkably. Making the deep recess into the moving table, moreover, needs many working steps. In addition, the moving table is made on the lower surface thereof with a raised side ridge that is used to set a slide unit in precise location on the moving table. This construction underneath the moving table would take even more complete processes to produce the moving table. The stationary bed is in the form of H-shape in transverse section, which is made on any one surface thereof with a recess to accommodate the armature windings therein while on another surface thereof with a recess to fit the drive circuit therein. Making the bed into the H-shape sophisticated in construction would also take much effort in working processes. Thus, the small sliding device with onboard linear motor first recited earlier is inconvenient for manufacturing at high production efficiency the small sliding device, which meets the requirements for high propulsion, high response and long traveling stroke.
With the sliding device disclosed in the second citation, which is also co-pending senior application of common assignment, the field magnets are arrayed in flush with one another on the underneath of the moving table. In the prior sliding device constructed as stated earlier, nevertheless, there is no way to install in place the field magnets of even more poles, for example eight poles to cope with the challenge to higher propulsion, higher response, longer traveling stroke, and so on. Moreover, the moving table is made on any one side thereof with a raised side ridge that is used to set a slider in precise location on the moving table. This construction would take even more complete processes to produce the moving table. In addition, the stationary bed is also made on the upper surface thereof with a deep recess to fit the armature windings into there. Cutting deep the recess into the bed would also take much effort in working processes. The bed in this prior sliding device is further cut away partially at lengthwise middle area on any one side of the bed to provide a space to install sensors therein. This also makes the bed in construction more complicated to need much additional working steps.
In recent years, meanwhile, a sliding device with onboard magnet-moving linear motor allowed to operate over a longer stroke is extensively required for use in diverse fields including the semiconductor manufacturing machines, various assembly machines, precise measuring/inspection machines, testing machines, machine tools, and so on. Thus, it remains a major challenge to further develop the sliding devices disclosed in the commonly assigned Japanese Patent application as recited earlier so as to allow the moving table operating over longer traveling stroke, enhancing the propulsion, traveling velocity, high response, and so on, even with small or compact in construction and better in production efficiency.